The present invention relates to a high performance rare earth-iron giant magnetostrictive material. More particularly, the present invention relates to a high performance rare earth-iron giant magnetostrictive material obtained by using an industry grade pure iron, instead of physically pure iron, such as electrolyzed pure iron or hydrogen reduced pure iron, as the iron source. The present invention also relates to a method of preparing the high performance rare earth-iron giant magnetostrictive material.
Magnetostrictive material, such as nickel, cobalt, iron and their alloys, undergoes, at room temperature and in a magnetic field, a change in shape along the magnetic field direction, referred to as magnetostriction. Their magnetostriction coefficient were only in the range of tens of ppm, though they were the main vibrative material of the transducer used previously. The researches in early 1960's have discovered that some heavy rare earth elements could result in a magnetostriction coefficient 1000 times larger than that of iron, and 200 times larger than that of nickel. However their functions could be performed only at a low temperature condition while at room temperature, the magnetostrictive performances of the said heavy rare earth elements are by far not as good as that of iron, nickel and cobalt. In early 1970's, it was found first by that the rare earth-iron alloys TbFe2, DyFe2 and SmFe2 have a giant magnetostriction at room temperature. However, these alloys have high magnetocrstalline anisotropy energy. Therefore, only in a high magnetic field could these alloys show high magnetostriction, resulting in a substantial difficulty in practical application. The researches in the later 1970's found that DyFe2 has a magneto crystalline anisotropy that is opposite to that of TbFe2 and SmFe2 alloy, and their anisotropies could compensate and counteract mutually. Accordingly, the oriented multi- or single crystalline tri-element alloy Tb—Dy—Fe and Sm—Dy—Fe, which have a giant magnetostriction even at a low magnetic field and at room temperature have been developed. U.S. Pat. No. 4,308,474, is a valuable and commercialized rare earth-iron giant magnetostrictive material and has been practically used until now. In this patent, disclosed in detail are the elements of the alloy, composition and crystal growth requirement, etc. This patent covers 6 basic alloys: TbxDy1-xFe2-w, TbxHo1-xFe2-w, SmxDy1-xFe2-w, SmxHo1-xFe2-w, TbxHoyDyzFe2-w, SmxHoyDyzFe2-w. Their crystalline axis directions are located within the range of 10° around the maximal magnetostrictive direction [1,1,1] of the crystal cell, wherein the oriented multi- or sing crystal material Tb0.3Dy0.7Fe1.95 is the sole commercialized rare earth-iron giant magnetostrictive material. A. E. Clark has described in detail in the authoritative work on the theory about rare earth-iron giant magnetostrictive material “Ferromagnetic Materials (Ed. by E. D. Wohlfarth)”, Vol. 1, North Holland, Amsterdam, 1980, PP531 the cubic Laves phase crystal structure and the magnetostriction theory. According to his theory, in the Laves phase, the atoms orientate in different crystallographic directions, and the direction [1,1,1] has the maximal atom density. Under the action of a magnetic field, the specific distribution of the electron cloud of the rare earth-iron atoms undergo a change, the strength of the interaction among the atoms also change, resulting in a change in the distances there between and therefore in a giant magnetostriction effect.
In this circumstance, if the crystallographic direction of the material is just the same to the [1,1,1] direction, the material could have a macroscopic giant magnetostriction effect, and therefore a maximal saturation magnetostriction coefficient. In practical application, as the preferably orienting directions during crystal growth will deviate from the direction [1,1,1] to certain extent in the solidification process of the rare earth-iron compound crystal in Laves phase, the saturation magnetostriction coefficient of the material will be 5% less than the maximum.
Nowadays, the so-called rare earth-iron giant magnetostrictive material means the alloy Tb0.3Dy0.7Fe1.95, which is a crystallographic material having a strict (Tb Dy)/Fe atomic ratio, and its performances are closely dependent on the crystallostructure (crystal orientation), and the structure of the crystal phase. Any change to the mutual ratios of the elements, substitution, or addition or reduction of the elements, entrainment of impurities or change of the crystalline direction will bring harm to the giant magnetostriction of the material. However, out of consideration of the costs for raw materials, the industrial production of the material may allow some substitute elements or existence of some entrained impurities; though they may cause some loss of magnetostrictive property, but they may greatly broaden sources of the raw materials and substantially reduce the costs for production of the material, and promote commercialization and application of the material.
U.S. Pat. No. 6,273,966 discloses a high performance rare earth-iron magnetostrictive material having the formula (RX1RX2 . . . Rx11)(My1My2 . . . My6)z, wherein R represents one to eleven rare earth elements selected from the group comprising La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Y; 0≦Xi≦1, i=1,2 . . . , 11 and x1+x2+ . . . x11=1; M represents one to six metal elements selected from the group comprising Fe, Mn, Co, Ni, Al, and Si; 0≦Yi≦1, i=1,2,3,4,5,6, and y1+y2+y3+y4+y5+y6=1; 1.8≦Z≦2.1. This patent specially defines the controlled contents of non-metal impurity elements O, N and C being in the ranges of atom percent of 0: 6011–34000 ppm, N: 575–4400 ppm, C: 939–21000 ppm. Known from the definition of the composition of the magnetostrictive material as disclosed, it allows existence of the non-metal imparities O, N and C within the above-mentioned amounts and of several rare earth-iron elements and transition metal elements. This means that some crude alloys, which could be cheaper and be in a comparatively lower purity, could be used to produce the manetostrictive material having satisfactory performances, so as to keep a balance between its performances and production costs of the material.
Chinese Patent No. ZL98101191.8 discloses a rare earth-iron giant magnetostrictive material having a main orientation in the direction [1,1,0] and a process for its preparation. This material has its chemical formula (Tb1-x-yDyxRy)(Fe1-z-pBZMP)Q, wherein R represents at least one of the 5 rare earth-iron elements Ho, Er, Sm, Pr, and Nd; M represents one to six of the 16 non-Rare earth metal elements Ti, V, Cr, Co, Ni, Cu, Zr, Ga, Al, Mg, Ca, Cd, In, Ag, Au, and Pt. The non-metal element B is indicated in the formula without any description about its source and function. According to the requirements set forth in this patent, all of the raw materials should be in purity in the range of from 99.0% to 99.99%, preferably from 99.5% to 99.8%. This patent is mainly aimed at obtaining in industrial scale a multi- or single crystal magnetostrictive material having a main orientation in the direction [1,1,0] by using the raw materials in a comparatively lower purity and by a specific production process. However, this patent still has some problems, such as the raw materials still need to be in a relatively high purity and is of a much-restricted availability, the process and apparatus for its production are still complicated, etc.
Therefore, there is still a strong demand for a high performance rare earth-iron giant magnetostrictive material that could be much cheaper, while guarantee good magnetostrictive performances.